Glass colorant composition

ABSTRACT

Colorant-enriched frit glass compositions of the following ingredients are disclosed together with methods of producing colored glasses using same:

United States Patent Inventors Appl. No.

Filed Patented Assignee Erwin C. Hagedorn Oregon;

Dallas P. Hall, Toledo, both of Ohio 21,397

Mar. 20, 1970 4 Division of Ser. No. 579,971, Sept. 16, 1966, which inturn is a continuation-in-part of Ser. No. 285,088, June 3, 1963,abandoned Nov. 9, l 971 Owens-Illinois, lnc.

GLASS COLORANT COMPOSITION 4 Claims, 1 Drawing Fig.

U.S. Cl

[5]] Int. Cl C03c 3/14, CO3C 3/08 [50] Field of Search lO6/54, 47, 48.49

[56] References Cited OTHER REFERENCES Jous et al. 2. Physical Chem.(l934) pp. 389- 392. B24 ADI Z45 Weyl- Coloured Glasses- London- Dawsons of Pall Mall (i959l-pp. Ill, 128, 180-18! Primary Examiner-Helen M.McCarthy Allorneys- Richard B. Dence and E. .l. Holler ABSTRACT:colorant-enriched frit glass compositions of the following ingredientsare disclosed together with methods of producing colored glasses usingsame:

. Ingredients Percent by weight Composition 2 (om position 3 Composition1 1 Less than 25% X.

' At least 2%.

go 20 40 a P0 fab .20 40 w f0 4,00 20 40 w f0 7170 GLASS COLORANTCOMPOSITION CROSS-REFERENCE TO RELATED APPLICATIONS The presentapplication is a division of application Ser. No.

579,971, filed Sept. 16, I966, which in turn is a continuationin-part ofapplicants formerly copending application Ser. No. 285,088, filed June3, 1963, and now abandoned. This invention relates to acolorant-enriched glass suitable for use in coloring a base glass and,more particularly, to .a colorant-enriched glass frit having a highconcentration of chromium oxides.

BACKGROUND OF THE INVENTION 1. Field of the Invention colorant-enrichedglasses suitable for forehearth addition, in frit or molten form, to acolorless base glass to form a composite color glass are known, as arecolorant-enriched glass frits containing chromium oxides. A number ofpatents disclosing such frits for making colored glasses and ultravioletabsorbent glasses, the latter having a specific concentration ofchromium oxide wherein the chromium is hexavalent, have been issued tothe assignee of the present application.

2. Description of the Prior Art Colorant-enriched glass compositions aredisclosed in Hagedorn 'U.S. Pat. No. 3,024,121 granted Mar. 6, 1962;Swain US. Pat. No. 2,923,636 granted Feb. 2, I960; and Babcock U.S. Pat.No. 3,0 24,l20 granted Mar. 6, I962.

In general, however, such frits as disclosed in these patents have highmelting temperatures and/or relatively high viscosities when molten, soas to present certain difficulties and disadvantages in the processesfor forming colored glasses. These include higher costs due to the needofincreased temperatures to melt the frit, volatilization and consequentloss of certain of the ingredients in the glass because of the hightemperature, increased tendency for the chromium and other colorantoxides at high percentages to crystallize and form inclusions in theresulting colored glass, and difficulty in thoroughly dispersing themolten frit throughout the molten base glass due to the relatively highviscosity of the molten frit. Solution and devitrification problems aregreatly increased, especially in the production of highly reducedchromium frits.

SUMMARY'OF THE INVENTION Accordingly, it is an object of the presentinvention to provide a colorant-enriched glass'composition suitable foruse in coloring a base glass, and which is free of the aforementioneddifficulties and disadvantages.

It is a further object of the present invention to provide a family ofcolorant-enriched glasses suitable for use in coloring a base glass,which glasses have low melting temperatures. low viscosities, and arereadily miscible with colorless molten base glasses to form uniformlycolored glasses.

It is another object of the present invention to provide glasses havinga high concentration of chromium oxides, i.e.. from about 2 to aboutpercent or more, and which, when added in frit or molten form to acolorless molten base glass, impart a yellow-green, green, or blue colorto the base glasses, and which, if desired. will also impart the abilityto absorb substantially all ultraviolet radiation to which it may besubjected.

In attaining the objects of the present invention, one feature residesin maintaining the silica content of the colorant-en riched glass at alow level while maintaining a high concentration of a mixture of alkalimetal oxides and B 0; wherein the total of the alkali metal oxides and B0 is from 44 percent to 74 percent by weight of the colorant-enrichedglass, which glass has a lower viscosity and is more readily misciblewith the molten base glass than conventional high-silica-coloring frits.

Another feature of the invention resides in forming a colorant-enriched.silica-free glass having a critical content of alkali metal oxides and B0 which glass can be formed at a temperature as low as from about l,200l,400 F., and which has a low viscosity relative to known highlycolorant-enriched glass frits, so that it can readily be added to andmixed with a molten base glass at the forehearth to produce a uniformcolor in the resulting glass article.

Other objects, features, and advantages of this invention will becomemore apparent from a reading of the following disclosure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Glass frits having the capacityto dissolve significant amounts of various colorant oxides such aschromium, cobalt, nickel, iron, zinc, manganese and copper, whilemaintaining a low viscosity have many advantages over frits of the priorart, including (1) making possible and practicable the formation ofhigh-chromium colored glasses such as emerald green, UL- TRASORB emeraldgreen, and champagne green; (2) reducing the amount of frit necessary toimpart the desired colors; (3) improving the mixing in the forehearthdue to lower viscosity and surface tension; (4) reducing the temperaturenecessary for melting the frit; and (5) making possible molten fritadditions from small electric furnaces above the forehearths.

It has been found that highly colorant-enriched glass compositionshaving the following essential ingredients are suitable for addition asfrits or in a molten state, to a molten colorless base glass at theforehearth:

In the above list, R 0 represents a mixture of Na,O and K,O, with thelatter being present in an amount less than percent by weight of theformer. The foregoing compositions can accommodate, withoutrecrystallization, more than 2 percent by weight of the various colorantoxides. Thus, the compositions of the invention contain more than 2percent chromium oxides in the vitreous state.

When colorant-enriched glass frits made in accordance with thisinvention are to be stored for any length of time prior to use, it hasbeen found that the presence of M 0; in the frit composition increasesthe chemical durability of the frit while simultaneously preventing theagglomeration of the frit particles. When forehearth frit additions aremade, it is important that the frit particles be free-flowing andreadily dispersible throughout the molten base glass. The presence ofasufficient amount of alumina, up to about l0 percent by weight of theglass frit composition, and preferably from 0.5 to 7 percent, preventsthe frit particles from adhering to each other during storage.

While the oxides of chromium are present, other metal oxides can also bepresent in the glass frit composition in the following amounts withoutmaterially affecting the ability of the frit to hold a high chromiumcontent, it being understood that the maximum amount of each should notbe present in the composition at the same time.

TABLE I Colorant-enriehod glasses, percent by weight Ingredients (A)(13) (C) (D) (E) (F) (G) (H) (1) (J) (K) S101. 40. 017 18.17 32. 54 23.51 40.01 22.87 41. 30 23. 6D 42. 81 22. 20 311. 61 1-203 4. 85 5. 36 5.35 5. 35 6. 59 6.821 8. 32 7.10 4. 62 8. 32 6. 65 NazO. 27. 13 33. 5844. 41 43. 75 26. 36 31. 84 30. 65 36. U5 2!). 17 40. 85 20. 42 Kg().1.50 1.66 1.66 1.66 1.10 2.15 2.58 4.311 3.53 2.58 4.12 B 011 22. 2!)37. X6 12. 47 22. Oil 21. 65 21. 36 11. 64 22. 01 11 0 20. 63 .10 16TABLE 11 Parts by weight Composition (A) (B) (D) (E) Raw nntterials:

Sillld 42. 1 20. 0 36. 2 26. 15 22. 1 I 1i). 6 36. i) 12. 08 26. 15 33.35 Soda tISh-.. 8 64 8 75 3 66. I 30. 81 33 7 39. 7 2 U4 66. i) 15. ()0BOl'ftX (de11yd.) 34 1 20 8 36.8 34.1 27 6 15.6 32 7 16 24 36 X 51) 0O11011 011101111129 5 78 6 )4 6 94: 6. )4 8 12 6 )5 8. 7 11 6 Potassiumdichromate- Cobalt oxide (C0 04) s Bol'lo acid (a11hyd.)

Calcium carbonate Ne hvlino syanite So ium Silicate (anhyd.) 47. Leadoxide (113 04) When the amounts of K 0, Na O and B 0 were outside ofwanted, one could add up to about 10 percent or more SiO to the rangesset forth above, attempts to make the colorant-enthe aforesaid listedcompositions as long as the ability of the riched glasses or frits wereunsuccessful due to the formation particular composition to accommodatethe desired amount of chromium oxide crystals in the glasses. ofchromium oxide in the vitreous state was not materially aflt has alsobeen found that high colorant-enriched glasses fecteduseful forforehearth addition to a molten base glass can be Practicing F Present")Ventlon, it is Often advantageous made without the presence of anysilica, and such glasses, useto adjust the 9 6 the fl'lt glass t pf tdensity of ful for addition as frits or by direct addition to theforehearth 40 the base g|a$5 m the Interest ofFfficlency g We h inmolten form, having the following essential ingredients: found that thlscan be acwmpllshed by Incorporating the ides of lead, barium, zinc, andmixtures thereof into the sodium borate frit composition. For instance,ordinary sodalime Ingredients Fem! by WWI" base glass has a density ofabout 25 gm./cc., while certain of Na 0 2 I40 the sodium borate fritsofthe invention have a density of about 2.4 gm./cc. It has been foundthat the density of the frit can be 3,0, 49-70 tailored to achieveoptimum mixing by incorporating up to 1 1 2 15 percent of the combinedoxides of ZnO, BaO and PbO into c (H0 the frit batch. In the idealsituation, the density of the frit will be numerically equal to orgreater than the density of the base 50 glass. Table Ill(a) belowillustrates the foregoing.

The total amount of Cr O in the vitreous state in the composition willvary from above 2 to about 10 percent or more.

. TABLE 111 (u) Mmor amounts of the followmg oxides may also be presentwithout materially affecting the low melting temperature or l t' l lviscosit of the above com osition 5 Column Em'chcd Glass re a we y ow yP 1 diems (Percent by Weight) (v) (W) (X) (Y) (Z) (AA) CO0 04% by weighNa,0 26.96 18.48 25.39 25.39 23.60 24.45 M110 048% by "1 111 K10 -594.73 4.59 13,0, 61.04 41.52 57.49 57.49 53.45 55.36 Cr 0 7.41 7.41 7.417.65 7.41 Illustrative examples of slllca-free, h1ghly colorant-ennched60 glasses coming within the scope of the invention are set forth 1 inthe following table: lino TABLE III Coloraut-emiched glasses (percent byweight) Ingredients (O) (P) (Q) Again, it is to be understood that themaximum amounts of ZnO 40.0 5.12

these added oxides are not to be present at one time. If one Pb, r

BaO l0.56

NiO

CuO

Den.gm,/cc. 2.376 2.778 2,476 2.435 2.544 2.537

In the absence of the oxides of chromium, the alkali borate system ofthe invention is an excellent vehicle for the forehearth addition ofother colorant metal oxides to a molten base glass. We have found thatthese alkali borate glasses, particularly the sodium borate glasses, arecapable of dissolving unexpected amounts of the oxides of nickel, iron,manganese, cobalt, zinc, copper and mixtures thereof. It will beunderstood that the maximum solubility of any particular colorant oxideoccurs when all other colorants are absent, even though significantamounts of the above-mentioned oxides can be dissolved together in asingle frit composition.

Usually these frits are within the composition range:

(wherein the combined colorant oxide content is at least 2 percent byweight).

It is usually preferred that at least 5 percent of the particularcolorant oxide be present in the frit to minimize the amount of frit tobe added to achieve the desired degree of coloration in the compositeglass.

In one embodiment of the present invention a single colorant oxide fromthe above list is present in the alkali borate frit. The amount ofcolorants will be at least 2 percent by weight and preferably 5 percentby weight of the frit composition. The maximum amount of colorant willbe that shown in the above table.

For instance, in the sodium borate system containing a single colorantoxide, the composition ranges are as follows:

Percent Broad Preferred (olorant oxide Component rangirange Nickel asthe single colorant B 35-70 40-65 N320 10-40 15-30 Nit) 2-18 -18 Iran asthe single colorant B 0] 35-70 40-65 N820 -40 -30 Manganese as thesingle colorant... Bzox 35-70 40-65 N 310 10-40 16-30 MnO 1-23 5-23Cobalt as the single colorant B; -70 -65 NagO 10-40 15-30 C00 2-43 5-43Zinc as the single colorant B 0 35-70 40-65 N 820 10-40 15-30 ZnO 2-435-43 Copper as the single co1orant B203 35-70 40-65 N8 0 10-40 15-30 CuO2-28 5-28 I Total iron. b Total man anese.

TABLE IIItb) (folormit-em'it-hed glasses (percent by weight.)

Ingredients (Ell) (CC) (1)11) (ICE) (FF) Density grim/cm".

The above frits were made by melting the following raw batch materials,cooling the melt and quenching on a steel plate.

When attempts were made to form silica-free, colorant-enriched glasscompositions containing chromium wherein the amounts of Na O and B 0were outside of the ranges set forth in tables lll or llla or lllb,chromium oxide crystals were formed in the glasses, which crystals wereextremely difficult to melt, even when the glasses were subjected tohigher temperatures. Due to such crystal formations, these glasses wereunsuitable for use as colorant additives to molten base glasscompositions.

The base composition of the silica-free frits may be Na B O which, inhydrate form (Na,B,O -5H O) is common borax. These frits can be meltedat very low temperatures, i.e., l,200-l,300 F. when potassium dichromateis used as the source of chromium. Such silica-free frits also havesurprisingly good chemical durability. Some have shown no signs ofweathering or caking over a period ofa year or two and, since they arenonhygroscopic, they always feel dry to the touch.

Since the solubility of hexavalent chromium exceeds the solubility oftrivalent chromium, making such frits suitable for use in producingcolored ultraviolet-absorbing glasses, it has been possible toincorporate reducing agents, such as sea coal, sucrose, iron scale,aluminum metal, into the composition so as to increase the amount ofCr Oat the expense ofCrO The total chromium oxide in the compositions setforth in the tables and the claims is expressed as Cr 0 f'All of thechromium oxide in the frit may be in the trivalent form (C50 or amixture of the trivalent with the hexavalent form (CrO The actual CrOcontent of any given frit is dependent upon two factors, namely l theaddition of the chromium to the frit batch as dichromate and (2) theoxidation state of the frit batch during melting. In certain examples,e.g., examples H, l, and K. all ofthe chromium was added as dichromate.

In other examples, the chromium was added as equal parts by weight ofpotassium dichromate and chromite, a mineral containing Feo-Cr O In themanufacture of ultraviolet-absorbent composite glasses, a residualhexavalent chromium content is desired, and an oxidizing agent such asniter is preferably added to maintain strongly oxidizing conditions inthe frit batch. A full discussion of the cr o cro, relation is to befound in Pat. No. 2,923,636 assigned to the assignee of the presentinvention,

The above colorant-enriched compositions in examples A-U, inclusive,were prepared by melting the batch ingredients at various temperaturesof from l,3002,500 F. for a time of from to l hour. The batches inexamples V through FF were melted at l,600 F. for l% hours. Platinumcrucibles were used in all instances, and an air atmosphere wasmaintained in the furnace.

ln forming a frit having a chromium content in a highly oxidized state,alkali dichromate is preferably utilized as the source of chromium. Whenthe chromium is added as an iron chromite or a mixture containing ironchromite, all of the iron must be completely oxidized before there canbe any hexavalent chromium in the glass composition. Frits which arerelatively high in hexavalent chromium (Cr-O are suitable for theforehearth production of ultraviolet-absorbing glasses, such asyellow-green, green, and blue glasses.

Low silica and silica-free glass frits wherein the chromium content isin the reduced state are produced by utilizing an alkali dichromate asthe source of chromium, and adding thereto a sufficient amount ofreducing agent such as carbon,

evident.

sugar, starch, powdered aluminum, iron scale, sea coal, etc., to convertthe hexavalent chromium to trivalent chromium. Combinations of sea coaland iron scale in the frit batch have produced high-chrome frits which,when added to molten flint glasses, produce an emerald green glasscomparable to the accepted standard emerald green. 10 Two frits havingthe chromium content in the reduced state are shown in the followingexamples:

l5 FRI'I GLASS COMPOSITION Weight percent Frit K Frit U 4.12 4.26 O;30.16 56.11 F010; (total iron) 8. 04 7. 76 CrzOa(totalchromiurn)....6.65 6.88 Batch Weights:

Sand 33.35 0 Borax (anhydrous). 50.00 100 Boric acid (anhydrous). 2. 290 Soda ash 15.00 0 Potassium dichromate" 14. 77 16.0 Iron scale 8.308.40 Sea coal. 2. 40 2.40

The batch ingredients were melted at a temperature of 2.000 F. for lhour. cooled and fritted. The frits were then added by forehearthaddition to a glass having the following composition:

Ingredients Percent by Weight sio, 72.12 1 1.74 CaO .29 MgO 1.15 -u,o13.34 K,o 0.32 rep, 0.04

The final colored glass had the following composition:

Percent by weight Glass with Glass with Frit K rlt Ingredients: s10, 7o.94 70.10 A120 1.60 1.69 Ga 10. 05 10.98- MgO. 1.12 1.12 N820. 13.5313.67 K70. 0.43 0013. B20 0.88 1.59 0 F9203(t0talilOI1). 0.26 0.22 CnO(total chromium).. 0.20 0.20 Analyzed constituents:

FeO (total iron) 1 0. 234 Foo 0. 002a ch0 .220 C.I.E. data (10 mm.).

Percent briglitness 35.4 23.8 Percent purity 63.0 75.0 Dominant wavelength in millimivrons. 555. 5 556.0

A typical emerald green glass has 35.0 percent brightness. 66.0 percentpurity, and a dominant wave length-p. of 555.0.

From the graph in the drawing, the similarity in wave length between anatural emerald green glass and glasses of the foregoing examples madewith Frits U and K will be readily Examples V and W in table lll(a)demonstrate how the density of the frits of the invention may vary withcomposition. Examples X through AA demonstrate how the density of thecolorant frit may be adjusted to approximate the density of thesoda-lime base glass through the use of the oxides of zinc. lead andbarium.

Exemplary frits BB through FF are sodium borate colorant fritcompositions, containing colorants other than chromium that are suitablefor coloring soda-lime silica base glasses. These frits are low meltingand are readily admixed with the base glass at forehearth temperaturesto produce uniformly colored composite glasses.

The use of frits BB through FF is demonstrated by the followingexamples:

An ordinary colorless soda-lime base glass of the compositron:

SiO; 72.4l% A1101 l.75% CEO I l. l0% MgO 0.9l% Na o 13.34% K20 0.44% mo.0.03%

was melted in an ordinary glass melting furnace according to the methoddescribed on page l9. Frit composition BB (table II!) was added to thebase glass at forehearth temperatures in the ratio of 6.7 pounds per tonof base glass. This addition was accomplished after the base glass hadissued from the melting tank into the forehearth at temperatures in therange of 2,300-2,600 F The resulting composite glass was yellow in colorand had the following composition and properties:

SiO, 72.08% Al,O L74; CHO l LOSZ MgO 0.9m Na,O 1.14m K,0 0.4m 8,0, 0.29'; Fe,0, 0.0m NiO 0.05'4

C.l.E Data 2 mm. thickness) '7: Brightness 74 i Purity ll Dominantwavelength 575m Frit composition DD (table lll) was added at the rate of25.3 pounds of frit per ton of base glass to the colorless sodalime baseglass described on page 22 by the forehearth method described above. Theresulting composite glass was light orange in color and had thefollowing composition and properties:

(.LE. Data (2 mm. thickness) Frit glass composition FF (table lll) wasadded to the colorless base glass described on page 22 by the methoddescribed above. The ratio of addition was 32.5 pounds of frit per tonof base glass. The resulting composite glass was blue green in color andhad the following composition and properties:

While a low-silica-containing, colorant-enriched glass composition,useful in frit or molten form to color a molten base glass has beengiven above, a preferred composition is as follows:

Ingredients Percent by Weight l8-4l 0,0, 4-10 mo 3 1-46 8,0, 21-37 Totalof R,O and B,O, l5-74 R has the same values as given above. and theother oxides, also discussed above with the disclosure of the broadcomposition, may be present in the same designated amounts.

From the above disclosure. colored glasses meeting the desired opticalproperties and standards, as recognized by the industry and as set forthin Hagedorn U.S. Pat. No. 3,024,12l and incorporated herein byreference. can readily be made using the apparatus and methods disclosedin the aforesaid patent. Other suitable apparatus and methods aredescribed in U.S. Pat. No. 3,057,175 to RR. Rough.

We claim:

I. A colorant-enriched glass composition suitable for use in coloring abase glass, said colorant-enriched glass composition consistingessentially of the following ingredients in the indicated percentages byweight:

and a minor amount of at least one of the oxides selected from the groupconsisting of ZnO. BaO and PbO, said amount not exceeding l5 percent byweight in aggregate.

2 A colorant-enriched glass composition suitable for use in coloring abase glass, said colorant-enriched glass composition consistingessentially of the following ingredients in the indicated percentages byweight:

Ingredients Percent by Weight Na o 2 l-3O K,0 0-? 5,0 49-70 Cr,O (totalchromium) 2-H) zno+sao+pbo 0-15 a minor amount of at least one of theoxides selected from the group consisting of ZnO, BaO and PbO, saidamount not exceeding 15 percent by weight in aggregate and a minoramount of at least one of the following oxides up to the maximum amountindicated:

Oxides Percent by Weight Fe,O 0-10 sio, 0-10 3. A colorant-enrichedglass composition suitable for use in coloring a base glass to form anultraviolet-absorbing glass, said colorant-enriched glass compositionconsisting essentially of the following ingredients in the indicatedpercentages by weight:

Ingredients Percent by Weight Nu,0 24.77 K,O 4.22 8,0 55.87 CHO, (totalchromium) 6.88 C00 346 4. A colorant-enriched glass composition suitablefor use in coloring a base glass to form an ultraviolet-absorbing glass.said colorant-enriched glass composition consisting essentially of thefollowing ingredients in the indicated percentages by UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,619,218 DatedNovember 9, 1971 Inventor(s) ERWIN C. HAGEDORN AND DALLAS P. HALL It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Col. 5 and A, above TABLE I" insert --The following are illustrative offrits coming within the scope of this invention.--; Col. 5 and 4, below"TABLE I" insert --The frits of Table I were prepared by melting thefollowing raw batch materia ls and quenching on a steel plate. --3 Col.5, line A8, before "O-lO" delete "c"; Table III(a), under "Y",opposite"K O, insert l.59--5 Col. 5, between lines 50 and 55, underPreferred Range in Iron as the Single Colorant", 2-18" should be 5-l8-5Table IV, under "N", opposite "K MnO "5.46" should be "54.6"; Col. 8,line A8, 'lw" should be--m -5 Col. 9, line 71, "w" should be rn C Col.10, line 68, after 597" add --r9a--3 Col. ll, line 12, after "A86" addCol. 11, line 25, "15" should be --52--; C01. ll, line 50, delete"[ZnO+BaO+PbO"5 same line, delete "O-l5]"; Col. 12, line 11, delete"[ZnO+BaO+PbO"; same line, delete "0-151".

Signed and sealed this 3rd day of July 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. Rene Te2tmeyer Attesting Officer ActinCommissioner of Patents M PC4050 ($69) USCOMM-DC BO376-P69 W U SGOVERNMENT PRINTING OFFICE I 19.9 O365-334.

2. A colorant-enriched glass composition suitable for use in coloring abase glass, said colorant-enriched glass composition consistingessentially of the following ingredients in the indicated percentages byweight: Ingredients Percent by Weight Na2O 21-30 K2O 0-7 B2O3 49-70Cr2O3 (total chromium) 2-10 (ZnO+BaO+PbO 0-15) a minor amount of atleast one of the oxides selected from the group consisting of ZnO, BaOand PbO, said amount not exceeding 15 percent by weight in aggregate anda minor amount of at least one of the following oxides up to the maximumamount indicated: Oxides Percent by Weight Fe2O3 0-10 CoO 0-8 MnO 0-18SiO2 0-10
 3. A colorant-enriched glass composition suitable for use incoloring a base glass to form an ultraviolet-absorbing glass, saidcolorant-enriched glass composition consisting essentially of thefollowing ingredients in the indicated percentages by weight:Ingredients Percent by Weight Na2O 24.77 K2O 4.22 B2O3 55.87 Cr2O3(total chromium) 6.88 CoO 8.26
 4. A colorant-enriched glass compositionsuitable for use in coloring a base glass to form anultraviolet-absorbing glass, said colorant-enriched glass compositionconsisting essentially of the following ingredients in the indicatedpercentages by weight: Ingredients Percent by Weight Na2O 24.90 K2O 4.26B2O3 51.11 Cr2O3 (total chromium) 6.88 Fe2O3 7.76